Straight forward port. Note: this is currently crashing deep down in
QtQuick. To circumvent the crashes it helps to disable the property
highlightFollowsCurrentItem in the listviews. This solves the problem
that QtQuick crashes on first loading. Unfortunately it still crashes
if one tries to invoke TabBox for the second time.
The existing desktop switcher becomes the first available layout called
"informative". For both variants of desktop switchers a new config key is
introduced to define the desktop switcher layout.
Desktop layouts are installed into a different directory than window
switcher layout and use a different service type.
For the moment it's basically a hidden config option as there are no
further layouts yet.
BUG: 296068
FIXED-IN: 4.11
REVIEW: 110021
